1. Field of the Invention
This invention relates to a method and apparatus for measuring intracranial fluid characteristics. In particular, the method comprises a ventricular catheter which can be positioned into a ventricle of the brain having a transducer tipped catheter positioned at one end of the catheter for measuring fluid compositions, hemodynamics and pressure waveforms of intracranial fluid. A groove placed within a needle retains the transducer tipped catheter and underlying wires and may also provide a subdermal path into which an in-dwelling catheter can be drawn.
2. Description of the Relevant Art
Cerebral spinal fluid (CSF) circulating within the subarachnoid space between the arachnoid matter and pia matter produces intracranial pressure. CSF exerts pressure on the meningeal membranes as well as on the brain itself. While CSF circulates in the subarachnoid space, it also exists in a ventricle of the brain.
Often it is desirable to measure the CSF pressure in the subarachnoid space or ventricular space whenever the rate of CSF production exceeds resorption When production does exceed resorption, there is a pressure increase of the CSF causing intracranial pressure (ICP).
Typically, there exists numerous methods in which ICP is monitored. A common method of measuring ICP is to install a subarachnoid screw (bolt) within a hole or burr drilled through the skull. The screw is placed into the subarachnoid space without penetrating the dura residing underneath the skull A pressure transducer is then attached to the outer end of the screw and monitoring can then proceed. The major advantage of this subarachnoid screw technique is that the dura or cerebrum is not penetrated and therefore subjects the patient to less risk of infection. A major disadvantage in the subarachnoid screw technique is that the bolt can sometimes become occluded leaving false pressure readings at the transducer. Furthermore, because readings are taken in the subarachnoid space external to the dura, fluid pressure is not taken directly where the pressure exists within the brain. Namely, subarachnoid pressure is indirect and sometime yields inaccurate pressure compared to that which exists in the brain tissue underneath the dura. Unless the pressure is taken directly within the ventricular brain matter itself, readings in the subarachnoid space are often susceptible to artifacts and generally less preferred than direct ventricular methods. Often, when drilling the burr hole necessary for placing the screw, pieces of bones remain positioned between the pressure transducer and the pressure source thereby causing artifacts or false, dampened pressure readings.
In an effort to overcome the problems associated with subarachnoid screws, subdural screws are often used by placing the screws through the burr hole to a point underneath the dura matter. Although the subdural screw provides a more accurate pressure sensor than does the epidural screw, it is more intrusive and may subject the patient to infection. The main disadvantage with the subdural screw is that in the case of critically elevated pressures this method fails due to compression of the subarachnoid space (loss of fluid coupling). Furthermore, when acute brain swelling occurs, the pressure at the surface of the brain is generally higher than the pressure inside the ventricle. Thus, while subdural screws achieve more accurate pressure readings than epidural screws, subdural screws still cannot achieve high fidelity readings found in placing the pressure transducer directly into the ventricular region.
While direct placement of a transducer into the ventricle allows accurate pressure readings inside the brain, ventricle placement is highly intrusive and leaves the patient susceptible to infection at the point of insertion. Ventricular placement requires penetration of the skull via a burr hole and insertion of the ventricular transducer through the burr hole and into the ventricle of the brain. The presence of a direct pathway through the burr hole opening from an outside environment directly into the brain ventricle causes substantial risk of infection entering through the burr hole.
In order to alleviate the risk of infection, subdermal routing of the in-dwelling, ventricular catheter is often necessary. Instead of allowing the ventricular catheter to exit the scalp directly above the burr hole, the catheter is routed or redirected from the outer extremity of the burr hole just below the scalp to a distal location. Once the rerouting is achieved, the scalp and underlying tissue is closed over the burr hole or passage thereby leaving no direct path for contamination to enter the burr hole. If contamination is to enter the burr hole, it must travel from the distal exit point of the catheter and along the catheter to the burr hole.
Although distally routed ventricular catheters help reduce the risk of infection entering the burr hole passage, typical catheters placed within the ventricle have a fluid-filled path or fiber-optic signal lines. When rerouting the ventricular catheter, the fluid-filled path or fiber-optic signal lines can become crimped. Crimping or pinch-off occurring during subdermal rerouting often causes a reduction in signal integrity. Fluid-filled paths or fiber-optic signal lines must the handled with care and cannot be sharply redirected or routed to distal location as is often necessary in intracranial ventricular catheter routing application. Accordingly, conventional fluid-filled or optic transducers of the present art produce false or inaccurate pressure readings caused by pinch-off during subdermal routing.